A repository for all code, analyses, results, and data related to the study:
Evolutionary shifts dramatically reorganized the human hippocampal complex
Journal of Comparative Neurology (2019)
Interactive report of all anaylsis results.
- Nash Family Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029
- Ronald M. Loeb Center for Alzheimer's Disease, Icahn School of Medicine at Mount Sinai, New York, NY 10029
- Department of Psychological & Brain Sciences, University of Louisville, Louisville, KY 40292
The hippocampal complex (HC) is central to long-term memory storage and retrieval as well as spatial navigation across many species. Notably, humans appear to have greatly enhanced or possibly unique HC-mediated capacities such as constructive episodic simulation. Key studies have shown that the human HC is disproportionately large amongst hominoids, but much remains unknown at the levels of evolutionary substructural reorganization and ecological selection. Here, we calculated relative sizes of 12 HC subregions in a diverse sample of 44 primate species. We then used a Bayesian phylogenetic method, selective regime analysis, to identify 27 separate evolutionary shifts in HC organization across 65 million years of primate evolution. Additionally, a series of multi-variate phylogenetic regressions using HC-related ecological variables as predictors (Diet Breadth, Population Density, Group Size, Home Range Size, and Residual Home Range) revealed that relative fascia dentata and CA1 size were both significantly predicted by species’ home range size (after correcting for body size). However, perhaps the most notable finding of this study was that the shifts in HC size and subregional organization in the human lineage were the largest seen in all of primate evolution, rendering modern humans with a HC that is a clear outlier amongst all non-human primates investigated here. Given the extensive literature confirming the relationship between HC organization and function, these selective shifts are likely to have played a significant role in the emergence of human-specific capacities, such as constructive episodic simulation.